Method for producing biodiesel

ABSTRACT

The present invention relates to a method for producing biodiesel comprising a step of generating fatty acid alkyl ester and glycerol by a transesterification of animal and vegetable oils and fats and fatty acid alcohols in the presence of porous materials. The method is characterized by a high response speed and high FAME conversion, and can be performed in a consecutive process. Further, according to the method, a high-purity fatty acid alkyl ester and glycol can be produced irrespective of the content of free fatty acids (FFAs). Further, since the method does not use a catalyst, the total processing time and cost can be reduced, and the method is environmentally friendly.

TECHNICAL FIELD

The present invention relates to a method for converting oils intobiodiesel (fatty acid methyl esters, FAMEs) through atransesterification reaction.

BACKGROUND ART

Currently, among biodiesel producing processes, only atransesterification reaction has been commercialized.

In such a method of conversion into biodiesel (fatty acid methyl esters,FAMEs) through a transesterification reaction, triglyceride is a basiccomponent of edible/non-edible oils that are used.

While FAMEs and glycerin are generated from triglyceride through thetransesterification reaction, its reaction rate is very slow. Therefore,acidic catalysts and/or basic catalysts are used to increase the rate ofthe transesterification reaction in the commercialized biodieselproducing process.

It is known that the reaction time to obtain a FAME conversion of 95%through a transesterification reaction is not less than 30 hours for anacidic catalyst and not less than 2 hours for a basic catalyst.Naturally, the use of the basic catalyst may be more favorable, but thefatty acids separated from triglyceride, that is, free fatty acids(FFAs) are problematic. Due to these free fatty acids, oils having ahigh acid value (1 or higher) cause a saponification reaction in atransesterification reaction using a basic catalyst. The free fattyacids are relatively easily generated from oils by an external stimulussuch as heat, solar light, or oxidation. Therefore, it may be consideredthat free fatty acids are present in all the oils used in the biodieselproducing process.

Currently, the commercialized biodiesel conversion process includes apretreatment process using an acidic catalyst (H₂SO₄) and a maintreatment process using a basic catalyst (KOH, NaOH).

The pretreatment process and the main treatment process require longreaction times of at least 30 hours and at least 2 hours, respectively.Since these pretreatment and main treatment processes are batchreactions, they are difficult to apply in the mass production of FAMEs.

Moreover, the commercialized biodiesel conversion process necessarilyentails a washing process using warm water due to the use of the acidiccatalyst and the basic catalyst. However, the washing process causes alarge amount of waste water and a loss of oils, which are reactants,resulting in remarkably deteriorating the overall process yield.

Moreover, when the above catalysts are used to produce mass biodiesel inthe commercialized biodiesel reaction process, a washing process and apurification and separation process take much time and cause a largeamount of waste water. A natural purification process not using acentrifuge takes at least one hour or usually two or more hours. Here,biodiesel may be washed out during the washing process and thepurification and separation process, resulting in reducing a biodieselproduction yield.

In order to solve the drawbacks due to the use of the above catalysts, asupercritical transesterification process has been studied that methanolor ethanol and an oil component are allowed to react at 120 to 150° C.at the high pressure conditions of 50 to 200 bar, thereby directlyobtaining fatty acid alkyl esters.

Although the supercritical transesterification process may collect fattyacid alkyl esters generated, a large amount of alcohol such as methanolor ethanol, however, is used such that the ratio of alcohols to oils isapproximately 20:1. Moreover, in the supercritical transesterificationprocess, continuous processing is difficult and production costsincrease due to high pressure conditions. Accordingly, the supercriticaltransesterification process corresponds to merely R&D-level technologyuntil now. Particularly, since the supercritical transesterificationprocess has lower energy efficiency due to the introduction of excessiveethanol, commercialization of the supercritical transesterificationprocess for biodiesel production still seems to have a long way to go.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

DISCLOSURE Technical Problem

An embodiment of the present invention may provide a method forproducing biodiesel having advantages of realizing mass production byemploying a continuous process.

An embodiment of the present invention may provide a method forproducing biodiesel having advantages of obtaining high-purity fattyacid alkyl esters and glycerol regardless of the content of fatty acidcontained in oils.

An embodiment of the present invention may provide a method forproducing biodiesel having advantages of preventing the generation ofwaste water and the drop in the yield of biodiesel during a washingprocess for removing an acidic catalyst or a basic catalyst.

An embodiment of the present invention may provide a method forproducing biodiesel having advantages of being environmentally friendlyand achieving a significant energy saving effect.

Technical Solution

An embodiment of the present invention started to be made from thethinking that a catalyst-free transesterification reaction may beinduced by supplying the heat energy higher than activation energynecessary for the reaction to reactants. In other words, it seems thatthe temperature may be a main driving force for the transesterificationreaction.

An embodiment of the present invention provides a method for producingbiodiesel, the method including generating fatty acid alkyl esters andglycerol by a transesterification reaction of oils and aliphaticalcohols in the presence of a porous material.

The temperature of the transesterification reaction may be controlledsuch that the transesterification reaction proceeds in the presence of aporous material, by raising energy levels of the oils and the aliphaticalcohols through a supply of heat energy.

The temperature of the transesterification reaction may be controlledsuch that the fatty acid alkyl esters are generated in a gas phase andthermal cracking of the oils is not generated.

The temperature of the transesterification reaction may be 350 to 500°C.

The retention time of the transesterification reaction may be 0.1 to 5minutes.

The weight ratio of the oils to the alcohols may be 1:0.05 to 1:1.

The transesterification reaction may be performed in the gas atmosphereof at least one of nitrogen, argon, or carbon dioxide.

The pressure of the transesterification reaction may be 10 mmHg to 10atm.

The transesterification reaction may be performed in a heterogeneousphase reaction.

The transesterification reaction may be performed in a continuousprocess.

The porous material may be at least one of alumina (Al₂O₃), zeolite,activated carbon, charcoal, or silica.

The porous material may include a mesoporous material, a macroporousmaterial, or both thereof.

An embodiment of the present invention provides a method for producingbiodiesel, the method including: inducing a transesterification reactionbetween oils and aliphatic alcohols by continuously supplying the oilsand the aliphatic alcohols into a reactor charged with a refractoryporous material; and collecting gas-phase fatty acid alkyl esters andglycerol, which are generated by the transesterification reaction.

In the inducing of the transesterification reaction, a purge gas may becontinuously supplied together with the oils and the aliphatic alcohols,the purge gas being at least one of nitrogen, argon, or carbon dioxide.

Advantageous Effects

According to an embodiment of the present invention, biodiesel may beeffectively mass-produced in a continuous process by atransesterification reaction of oils and aliphatic alcohols in thepresence of a porous material. Further, since an acidic catalyst or abasic catalyst is not used, harmful effects due to the use of the acidiccatalyst and the basic catalyst may be prevented.

Particularly, since the method for producing biodiesel without catalystsaccording to an embodiment of the present invention eliminates a washingprocess, the method may be environmentally friendly and have an energysaving effect producing high-purity fatty acid alkyl esters andglycerol. Further, according to an embodiment of the present invention,waste water treatments due to the washing process, which is caused bythe use of catalysts, is not performed, thereby saving the total processtime and cost for producing biodiesel and producing regenerative fuelsthrough a more environmentally friendly process.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a table showing a fatty acid profile of oils according to anembodiment of the present invention;

FIG. 2 is a schematic view showing a mechanism of a transesterificationreaction according to an embodiment of the present invention;

FIG. 3 is a schematic view showing a mechanism of a transesterificationreaction using MeOH according to an embodiment of the present invention;

FIGS. 4A to 4C are graphs showing pore distributions of activatedalumina, cordierite, and charcoal, respectively;

FIG. 5 is an image showing biodiesel (FAMEs, in the left flask) andglycerin-separated biodiesel (FAMEs, in the right flask), which wereobtained through a catalyst-free continuous type transesterificationreaction according to an embodiment of the present invention;

FIG. 6 is a graph showing thermo-gram and differential thermo-gram (DTG)of soybean oil according to an embodiment of the present invention;

FIG. 7 is a graph showing the FAME conversion depending on control ofthe temperature according to an embodiment of the present invention;

FIG. 8 is a table showing boiling points of FAMEs according to anembodiment of the present invention;

FIG. 9 is a graph showing the FAME conversion depending on control ofthe mixture ratio of MeOH and oils according to an embodiment of thepresent invention;

FIG. 10 is an SEM image of charcoal as a porous material according to anembodiment of the present invention;

FIG. 11 is a graph showing the FAME conversion when carbon dioxide ornitrogen was used;

FIG. 12 is a graph showing the FAME conversion for an example in which100% of fatty acid was used in the reaction according to an embodimentof the present invention;

FIG. 13 is a graph showing the FAME conversion when charcoal was usedaccording to an embodiment of the present invention (Example 12);

FIG. 14 is a graph showing the FAME conversion when ethanol (EtOH) wasused according to an embodiment of the present invention (Example 14);

FIG. 15 is a graph showing the FAME conversion using a thermo-chemicalmethod of the related art (Comparative Example 3); and

FIG. 16 shows a mass chromatogram for products which were obtained aftera transesterification reaction was performed using beef tallow and lardin Example 16.

MODE FOR INVENTION

According to an embodiment of the present invention, there is provided amethod for producing biodiesel, the method including generating fattyacid alkyl esters and glycerol by a transesterification reaction of oilsand aliphatic alcohols in the presence of a porous material.

Hereinafter, methods for producing biodiesel, in which oils areconverted into fatty acid alkyl esters through a transesterificationreaction according to embodiments of the present invention, will bedescribed in more detail. However, these embodiments are provided merelyfor illustrating the present invention, and it will be apparent to thoseskilled in the art that the scope of the present invention is notlimited by these embodiments and various modifications of theembodiments may be made within the scope and technical range of thepresent invention.

Further, unless particularly mentioned herein, the term “including” or“containing” refers to including some elements (or components) withoutany limitation, and should not be construed as excluding addition ofother elements (or components).

In the procedure of repeated researches about the production ofbiodiesel from oils through a transesterification reaction, the presentinventors found that the use of a porous material without theintroduction of a separate catalyst may lead to the production ofhigh-purity fatty acid alkyl esters and glycerol in a continuous type,not in a bath type, regardless of the presence or absence, the content,or the kinds of free fatty acids (FFAs) contained in oils, and thencompleted an embodiment of the present invention.

According to an embodiment of the present invention, atransesterification reaction is induced by a thermo-chemical conversionmethod. According to an embodiment of the present invention, neitherliquid nor solid catalysts are needed and high-pressure supercriticalconditions are not required.

The present inventors determined that the reaction temperature may be amain driving force for a transesterification reaction, and thought thatthe activation energy of the transesterification reaction may besufficiently reached by the supply of heat energy. The present inventorsnoticed that the activation energy of the transesterification reactionis lower than those of other catalytic reactions such as methane steamreforming and the like.

The present inventors determined that a catalyst-freetransesterification reaction is possible through a heterogeneousthermo-chemical process. Here, the heterogeneous thermo-chemical processincludes reactions occurring between liquid-phase oils and gas-phasealcohols at a high temperature. However, the allowable temperature rangefor a catalyst-free transesterification reaction is uncertain.Therefore, thermo-gravimetric analysis (TGA) was performed on the oilsto investigate the allowable temperature range. The results are shown inFIG. 6. The thermo-gravimetric analysis associated with FIG. 6 will belater described in detail.

The present inventors tried a catalyst-free transesterification reactionin the temperature range which was investigate through thethermo-gravimetric analysis, but aliphatic alkyl esters were notsignificantly converted. From the judgment of the present inventors, thereason is that the contact time between the liquid-phase oils and thegas-phase alcohols is short. Thus, the present inventors used a porousmaterial having tortuosity and adsorption capability in thecatalyst-free transesterification reaction in order to increase thecontact time of the heterogeneous phase reactants.

According to one embodiment of the present invention, thetransesterification reaction is induced by raising energy levels of thereactants through the supply of a heat source and using a porousmaterial, unlike a transesterification reaction using a catalyst in therelated art. Therefore, according to an embodiment of the presentinvention, biodiesel may be obtained even when only alcohols (MeOH,EtOH, etc.) and oils are used as reactants without an additionalcatalyst.

According to an embodiment of the present invention, the oils includemicroalgae oils as well as edible and non-edible oils. The oils includeall of oils or fats including triglyceride, and include even their freefatty acids (FFAs). Particularly, the oils may include triglyceriderepresented by Chemical Formula 1.

wherein,

R¹, R², and R³ are the same as or different from each other, and eachmay be a C₄-C₃₈ aliphatic hydrocarbon group, preferably a C₄-C₂₄aliphatic hydrocarbon group, or more preferably a C₁₂-C₂₀ aliphatichydrocarbon group. The number of carbon atoms of the aliphatichydrocarbon group in the triglyceride may be optimized to be similar tothat in the general diesel.

Physical and chemical properties (viscosity, molecular weight, boilingpoint, etc.) of the oils may be varied depending on the kinds of fattyacids (FAs) present in triglyceride, in other words, the kinds ofsubstituents R¹, R², R³ or the like in Chemical Formula 1. The fattyacid profile for representative components of the oils are asexemplified in FIG. 1.

In addition, examples of the oils may be ones including triglyceriderepresented by Chemical Formula 2 below.

According to an embodiment of the present invention, the oils mayinclude small amounts of other impurities or water. Particularly,according to an embodiment of the present invention, atransesterification reaction may be effectively performed even when thereactants contain water. For example, even while the used cooking oilmay contain a large amount of water or even the non-edible cooking oilmay contain a slight amount of water, these oils, as they are, may beused in the transesterification reaction according to an embodiment ofthe present invention, without a moisture removal process. However, forsome kinds of oils, a content of water may be minimized within anappropriate range in order to attain more improved process efficiency.

Examples of the oils according to an embodiment of the present inventionmay include palm oil, soybean oil, rapeseed oil, corn oil, rape oil,sunflower oil, safflower oil, cottonseed oil, sesame oil, perilla oil,rice bran oil, palm kernel oil, camellia oil, castor oil, olive oil,coconut oil, almond oil, jatropha oil, diatom, sewage sludge,microalgae, beef tallow, lard, sun, fish oil, whale oil, tuna oil, andthe like. In addition, one or more of these oils may be used in amixture thereof, and their waste oils may be also used.

According to an embodiment of the present invention, aliphatic alcoholsor primary alcohols as a reactant may be used together with the oils.For example, C₁-C₁₂ aliphatic alcohols may be used. Examples of thesealiphatic alcohols may include methanol, ethanol, propanol, butanol,pentanol, and the like. One or more of these alcohols may be used in amixture thereof.

Of the alcohols, methanol and ethanol may be preferable in the view ofcosts. In consideration of reactivity, methanol may be more suitablethan ethanol. In the case of methanol (MeOH), the reactivity in thetransesterification reaction may become better due to reactivity andsteric factors of methanol. In addition, alcohols having many carbonatoms may be used to increase the number of carbon atoms in thegenerated FAMEs. Particularly, the use of various kinds of alcoholshaving different carbon atoms may variously change physical propertiesof the generated FAMEs.

In the reaction of the oils and the alcohols, the weight ratio of theoils to the alcohols may be within the range of 1:0.1 to 1:1, preferably1:0.15 to 1:1, and more preferably 1:0.2 to 1:1. In some cases, theweight ration of the oils to the alcohols may be 1:0.05. In addition,the alcohols may be used in a content of 10 parts by weight or more,preferably 15 parts by weight or more, and more preferably 20 parts byweight, based on 100 parts by weigh of the oils. In the aspect ofstoichiometry, the content of the alcohols is preferably 10 parts byweight or more based on 100 parts by weight of the oils. Alternatively,a large amount of alcohols may react with the oils, but in the aspect ofenergy efficiency, the alcohols may react with the oils while the useamount of alcohols is minimized. Alternatively, more than 100 parts byweight of the alcohols may be used based on 100 parts by weight of oils.However, the present inventors found that the excess use of alcoholsmerely increased the process cost but did not obtain significantimprovement in effects.

When the method of using an acidic catalyst or a basic catalyst or thesupercritical transesterification method is applied in the related art,the use of about 10 parts by weight of alcohols based on 100 parts byweight of oils never induced a transesterification reaction forgenerating biodiesel or required a reaction time of at least two hours.However, according to an embodiment of the present invention, even whenusing a small amount of alcohols as described above, a conversion ofapproximately 90% or higher, 95% or higher for appropriate reactionconditions, and 98% or higher for more appropriate reaction conditionsmay be obtained in a short time of 5 minutes or less, or approximatelyless than 1 minute based on experimental results confirmable by thepresent inventors. Particularly, an embodiment of the present inventionis characterized by using a remarkably small amount of alcohols ascompared with the biodiesel conversion process of the related art.

An embodiment of the present invention is characterized by allowing acatalyst-free transesterification reaction using the oils and thealiphatic alcohols in the presence of a porous material, instead ofusing an acidic catalyst or a basic catalyst like in the related art.According to an embodiment of the present invention, the porous materialdoes not function as a catalyst, which is clearly differentiated from asolid-phase catalyst.

The porous material according to an embodiment of the present inventionmaintains its porosity even in a thermo-chemical conversion procedure,in other words, a high-temperature transesterification reaction. Forexample, the porous material may be not thermally decomposed within thereaction temperature range according to an embodiment of the presentinvention. In this regard, it is explained that that the porous materialaccording to an embodiment of the present invention is refractory or theporous material according to an embodiment of the present invention iscalled a refractory material.

The refractory porous material according to an embodiment of the presentinvention may receive an activated reactant, and may be any porousmaterial having pores in which the reaction between the oils and thealcohols may be effectively performed. Alcohols evaporated due to thehigh temperature have an increased kinetic energy, and thus collide withthe oils adsorbed on the pores. As a result, a transesterificationreaction may promptly proceed. The reaction mechanism will be describedin more detail with reference to FIG. 3.

The refractory porous material according to an embodiment of the presentinvention may have various pore sizes and pore distributions in theconditions allowing evaporation and adsorption of reactants. Forexample, as the refractory porous material, a mesoporous material (porediameter: not smaller than 1 nm but smaller than 50 nm) or a macroporousmaterial (pore diameter: not smaller than 50 nm but not larger than 500μm) may be used. However, in the view of optimization of the reactorsize and improvement in process efficiency, the refractory porousmaterial may have pores with an average diameter of not smaller than 1nm or not smaller than 1 nm but not larger than 500 μm, preferably notsmaller than 1.5 nm, and more preferably not smaller than 2 nm.

For the understanding of the size or shape of pores of the porousmaterial according to an embodiment of the present invention, someexamples are shown in FIGS. 4A to 4C. FIG. 4A shows a pore distributionof activated alumina, and FIGS. 4B and 4C show pore distributions ofcordierite and charcoal, respectively. As shown in FIGS. 4A to 4C, it isdetermined that the dominant pore size, in other words, the pore size,at which the largest density or peak is shown in each pore distributioncurve, is approximately 10 nm or larger.

As above, the present inventors illuminated that the use of the porousmaterial was considered in order to increase the contact time betweenthe oils and the alcohols in the reaction conditions according to anembodiment of the present invention. Since the average molecular size oftriglyceride is approximately 2 nm, it is determined that pores having asize of at least 2 nm need to be dominant in the porous materialaccording to an embodiment of the present invention, in order to allowtriglyceride to be adsorbed or contained in the pores and allow atransesterification reaction between the oils and the alcohols tosmoothly proceed in the pores.

It is difficult to clearly define the porous material according to anembodiment of the present invention in a qualitative manner by using thepore size. However, based on experiment results so far, the presentinventors confirmed that a porous material, which may be generallycalled a mesoporous material or a macroporous material, may be used asthe porous material according to an embodiment of the present invention.Considering FIGS. 4A to 4C, a porous material having a dominant poresize of 10 nm or larger may be preferable.

Since a carrier for high-temperature (higher than 500° C.), which isgenerally used for a catalytic reaction or the like, is subjected tosintering treatment, its pores may be closed or smaller during thesintering treatment. In an embodiment of the present invention, whenthis conventional carrier is used, the amount of mesoporous materials isrelatively decreased, and thus a more amount of filler is needed and thesize of the reactor may be excessively enlarged. Particularly, in thecase of the sintered carrier of the related art, in other words, thesintered carrier of a microporous material having nano-sized pores, aneffective reaction of an embodiment of the present invention may be notexhibited even when a more amount of filler is introduced into thecarrier. In this regard, according to an embodiment of the presentinvention, a refractory porous material in which mesopores account for80% or more of the overall pores may be used.

According to an embodiment of the present invention, any refractoryporous material known until now may be used, and even a brick havingpores, or the like, may be used. Examples of the refractory porousmaterial may include alumina (Al₂O₃), zeolite, activated carbon,charcoal, silica, and a mixture and a combination thereof.

Further, according to an embodiment of the present invention, a catalystmay not be used, but a porous material doped with specific metals orinorganic materials may be used. For example, a refractory porousmaterial, which is doped with at least one metal component selected fromAg, Au, Na, Mg, Ca, Pt, Rh, Zn, Co, Cu, Rh, and the like, may be used.However, according to an embodiment of the present invention, it wasconfirmed that the use of a metal-doped porous material did not increasethe FAME conversion. Further, when a porous material is doped with ametal component or the like, the amounts of C₁₂-C₂₀ hydrocarboncompounds, which are within the range of diesel, aromatic compounds, orthe like, may somewhat increase due to cracking of oils.

The transesterification reaction according to an embodiment of thepresent invention is characterized by the application of the minimumheat such that oils as reactants may reach activation energy by onlyheat energy without thermal cracking of the reactants. In this regard,the reaction temperature of the transesterification reaction accordingto an embodiment of the present invention, for example, the temperatureof the reactor may be preferably 350 to 500° C. As may be confirmed inFIGS. 11 and 14 and descriptions thereof, the reaction temperature ofthe transesterification reaction according to an embodiment of thepresent invention may be extended to about 250° C. while the conversionmay be lowered or the reaction time may be lengthened. However, it isdetermined that the upper limit of the reaction temperature ispreferably controlled to be lower than 550° C. For example, thermalcracking of the cooking oil was observed at 550° C.

Further, the transesterification reaction according to an embodiment ofthe present invention may be employed in the conditions of normalpressure, in which the conversion was excellent. From experimentalexamples by the present inventors, the transesterification reactionaccording to an embodiment of the present invention seems to be notlimited by the pressure. For example, the reaction was possible even inthe conditions of high pressure or reduced pressure. However, the normalpressure may be more advantageous in the view of process efficiency andcosts. The reaction pressure according to an embodiment of the presentinvention may be, for example, 10 mmHg to 10 atm, preferably 0.5 to 5atm, and more preferably 1 to 5 atm.

The transesterification reaction may be performed at the foregoingtemperature and pressure conditions while the retention time is 0.1 to 5minutes, 0.2 to 4 minutes, or 0.3 to 3 minutes. Particularly, thetransesterification reaction according to an embodiment of the presentinvention may be performed for a retention time of 0.1 minutes or morein order to effectively increase the energy levels of the oils and thealcohols as reactants in the presence of the refractory porous material,and allows efficient evaporation and adsorption of the reactants.However, the retention time may be controlled to be 5 minutes or less toprevent the prolongation of the reaction time and the reduction inreactivity. Understandably, the retention time in thetransesterification reaction according to an embodiment of the presentinvention may be appropriately selected depending on the design of thereactor structure. In an embodiment of the present invention, thisreaction time is significantly reduced as compared with at least twohour, which is needed for pretreatment and main treatment processes whenan acidic catalyst and a basic catalyst are used in the related art, andthus very excellent process efficiency may be achieved. Further, thisretention time exhibits very excellent process efficiency as comparedwith a reaction time of about 5 to 20 minutes in a supercriticaltransesterification reaction that is known to be under development inthe current research stage.

The transesterification reaction according to an embodiment of thepresent invention may be performed in a heterogeneous reaction of liquidand gas phases in the presence of the porous material. In the reactionconditions according to an embodiment of the present invention, the oilsare determined to have a liquid phase, but not necessarily so. Sincealcohols having a low melting point are in a gas phase at thecorresponding conditions, the transesterification reaction according toan embodiment of the present invention seems to be performed in a mannerin which gas-phase alcohols react with liquid-phase oils to generategaseous FAMEs. Since triglyceride, which is a main component of theoils, is present in a liquid phase or gas phase, the triglyceride iseasily adsorbed on the porous material, and its energy level may beincreased by a heat source. The activation energy of thetransesterification reaction may be sufficiently reached by the heatsource.

The catalyst-free continuous type reaction according to an embodiment ofthe present invention may produce FAMEs even without purge gas, but thepurge gas may be used to control the retention time of the reaction andinduce a smooth continuous process. As the purge gas, an inactive gas isgenerally used, and for example, at least one of nitrogen (N₂), argon(Ar), carbon dioxide (CO₂), or the like may be used. This purge gas maybe supplied into the reactor together with the reactants such as oilsand the like.

According to an embodiment of the present invention, carbon dioxide(CO₂) or a gas containing at least carbon dioxide may be preferable asthe purge gas. As a result of the transesterification reaction accordingto an embodiment of the present invention, a coking phenomenon may occurin the porous material. This coking phenomenon may disturb thecontinuous transesterification process according to an embodiment of thepresent invention. However, carbon dioxide used as the purge gassignificantly reduces the coking phenomenon. When carbon dioxide is usedas the purge gas, the conversion of fatty acid alkyl esters may besomewhat improved in the catalyst-free transesterification reactionaccording to an embodiment of the present invention. As may be confirmedin FIG. 11, the use of carbon dioxide as a purge gas may increase theFAME conversion by about 3-4% as compared with the use of the otherpurge gas.

In the method for producing biodiesel according to an embodiment of thepresent invention, the transesterification reaction may be performed ina continuous process. In the process for producing biodiesel in acontinuous type according to an embodiment of the present invention, thetransesterification reaction may be continuously performed when oils andaliphatic alcohols are continuously supplied into a reactor in which arefractory porous material is present. In most cases, the reactor ispreviously charged with the refractory porous material while therefractory porous material is immobilized, but in some cases, therefractory porous material may be continuously supplied into the reactordepending on the kind of the reactor.

According to an embodiment of the present invention, a biomass havingpores itself may be used as a porous material. An example thereof isdisclosed in Koran Patent Application No. 2011-0101961, filled by thepresent inventors, the disclosure of which is incorporated herein byreference.

According to an embodiment of the present invention, since only oils andaliphatic alcohols react with each other without catalysts in thepresence of the foregoing porous material to produce biodiesel, theobtained biodiesel may have minimized impurities and high purity. Here,the conversion may also have a significantly improved degree as comparedwith the related art.

The fatty acid alkyl esters generated through the transesterificationreaction according to an embodiment of the present invention may containan aliphatic moiety having 10 to 24 carbon atoms, preferably 12 to 22carbon atoms, and more preferably 14 to 20 carbon atoms.

The transesterification reaction according to an embodiment of thepresent invention is shown in Reaction mechanism 1 below.

wherein, R¹, R², R³, R^(1′), R^(2′) and R^(3′) are the same as ordifferent from each other and each may be a C₄-C₃₈ aliphatic hydrocarbongroup, preferably a C₄-C₂₄ aliphatic hydrocarbon group, and morepreferably a C₁₂-C₂₀ aliphatic hydrocarbon group.

Hereinafter, the process for producing biodiesel according to anembodiment of the present invention will be described in detail withreference to the accompanying drawings such that the present inventionmay be easily implemented by a person having ordinary skill in the art.

First, as shown in FIG. 2, the process for producing biodiesel accordingto an embodiment of the present invention is characterized by using aporous material.

As shown in FIG. 3, the kinetic energy of evaporated MeOH which ispresent in pores or on a bulk phase increases due to a high temperature.MeOH having improved activity collides with triglyceride adsorbed on orcontained in the pores to induce a transesterification reaction. FAMEsand glycerin, which are reaction products, are released from a reactorwhile they are in a gas phase due to the reaction temperature. Thesegas-phase reaction products may become high-purity FAMEs and glycerinthrough only condensation thereof. It is known that glycerin may beeasily separated from FAMEs.

An example of a mixture of FAME and glycerin (left part) and an exampleof glycerin-removed FAME (right part), which are prepared according toan embodiment of the present invention, are comparatively shown in FIG.5. The two flasks of biodiesel shown in FIG. 5 were obtained by usingactivated alumina (Al₂O₃), and may be confirmed to exhibit an FAMEconversion of 99% at 400° C.

According to an embodiment of the present invention, the retention timeof reactants supplied into the reactor for a continuous process does notexceed even one minute. According to an embodiment of the presentinvention, the transesterification reaction is completed within oneminute to generate gas-phase products, which are then simply collectedand purified to obtain FAME. As described above, the fast reaction rateof the transesterification reaction according to an embodiment of thepresent invention enables the design of a process for producingbiodiesel in a continuous type. Since the retention time is determineddepending on amounts of purge gas and MeOH, the reaction rate may becontrolled by the purge gas.

In addition, the optimization of the catalyst-free continuous typetransesterification reaction according to an embodiment of the presentinvention depends greatly on the boiling point of triglyceride and theboiling point of FAMEs.

According to an embodiment of the present invention, the reactiontemperature of the process for producing biodiesel is designed such thatoils, in other words, triglyceride receives a heat energy which is notsmaller than an activation energy necessary for the reaction but doesnot allow thermal cracking, and such that FAMEs are present in a gasphase at the corresponding reaction temperature. Here, the oils are in aliquid phase, and alcohols having a low boiling point may be in a gasphase.

In order to obtain an appropriate reaction temperature in the processfor producing biodiesel according to an embodiment of the presentinvention, the thermo-gravimetric analysis (TGA) was conducted as shownin FIG. 6. The thermo-gram shown in FIG. 6 was obtained by using athermo-gravimetric analyzer by the NETZSCH Inc. Experiment was conductedfrom 20 to 1,000° C. at a heating rate of 100° C./min at the Aratmosphere. FIG. 6 shows the mass change depending on the temperatureand differential thermo-gram (DTG) obtained by primary differentiationof the mass change.

As shown in FIG. 6, triglyceride of the soybean oil has a boiling pointof about 405.2° C., and its mass change reaches the maximum value at452° C. as seen from the DTG curve. Therefore, considering the resultsof FIG. 7, the reaction temperature of a biodiesel conversion processusing triglyceride of the soybean oil may be preferably about 350-400°C. or 350-450° C. When the reaction temperature is excessivelyincreased, triglyceride may be unnecessarily evaporated and thus itsevaporation latent heat may induce an energy loss. As described above,the upper limit of the reaction time is controlled to be lower than 550°C. and preferably not higher than 500° C. such that thermal crackingdoes not occur.

Further, in order to reduce the energy loss due to condensation of FAMEsobtained through an embodiment of the present invention and theevaporation latent heat of triglyceride, the reaction temperature ispreferably 350° C. or higher. This will be easily understood fromboiling points of representative FAMEs shown in FIG. 8. Fatty acids ofmost oils shown in FIG. 8 have 14 to 20 carbon atoms (C₁₄-C₂₀). In orderto obtain C₁₄-C₂₀ FAMEs, which are generated from the reaction accordingto an embodiment of the present invention, in a gas phase without acondensation procedure, the reaction temperature is preferably 350 to500° C. and more preferably 350 to 450° C. Considering that the boilingpoint of MeOH is 65° C., gas-phase FAMEs may be easily separated. Thereaction temperature may be preferably 350 to 500° C. and morepreferably 350 to 450° C. since energy may be saved in a purificationprocess. Further, as summarized in FIG. 8, the boiling point ofarachidic acid methyl ester is about 215 to 216° C., but this value isobtained at 10 mmHg but not normal pressure. Therefore, the biodieselconversion process requires a temperature of 50° C. or higher. However,the excessive increase in the reaction temperature may maximize theenergy loss due to the evaporation latent heat of triglyceride, which isnot recommendable.

An example of the FAME conversion depending on the temperature change inthe transesterification reaction is shown in FIG. 7. The reaction wasperformed at atmospheric pressure. Activated alumina (Al₂O₃) was used asa porous material. The weight ratio of MeOH to oil was about 0.2:1. Asshown in FIG. 7, a high FAME conversion of 98% to 99% could be obtainedat a reaction temperature of 350° C. or higher. In addition, as shown inFIG. 7, the transesterification reaction according to an embodiment ofthe present invention is possible even at a temperature of 350° C. orlower. In this case, however, the FAME conversion may be somewhatdecreased to 90% or lower, and the reaction time may be somewhatlengthened.

Meanwhile, in the catalyst-free continuous type transesterificationprocess according to an embodiment of the present invention, thereactants are triglyceride and MeOH. The weight ratio of MeOH totriglyceride as the reactants is preferably 0.1:1. This value iscalculated in the view of stoichiometry and may be confirmed in FIG. 9.

For optimization of oils, that is, triglyceride, and MeOH in the processaccording to an embodiment of the present invention, experiments wereconducted for various weight ratios of MeOH to triglyceride. In theexperiment in FIG. 9, a transesterification reaction for biodiesel wasperformed at a temperature of 400° C. and at atmospheric pressure, andcharcoal was used as a porous material. As shown in FIG. 9, it may beseen that the FAME conversion was very excellent at a MeOH percentage ofpreferably 20% or more. Even when another porous material according toan embodiment of the present invention, for example, activated alumina(Al₂O₃) was used, nearly similar results as shown in FIG. 9 wereobtained.

FIG. 11 is a graph showing that the FAME conversion was increased whencarbon dioxide was used as a purge gas. The experiment for FIG. 11 wasconducted at atmospheric pressure, activated alumina as a porousmaterial and methanol as alcohol were used.

In addition, FIG. 12 is a graph showing the FAME conversion according tothe purge gas while 100% of fatty acid was used for the reaction. In theexperiment for FIG. 12, activated alumina as a porous material, methanolas alcohol, and oleic acid as oils were used at atmospheric pressure. Itwas seen from FIG. 12 that, even when 100% fatty acid having an acidvalue of approximately 200 was used in this experiment, the FAMEconversion was about 90% or more at a temperature of about 400° C. orhigher.

According to an embodiment of the present invention, the reactionresults when charcoal was used instead of activated alumina (Al₂O₃), asa porous material, are shown in FIG. 13. Here, the weight ratio of MeOHto oil was 0.2:1 and the experiment temperatures were 350° C., 400° C.,and 450° C. The porous structure of charcoal may be confirmed from theSEM image of FIG. 10. Meanwhile, it may be confirmed from FIG. 9 that ahigh conversion was obtained by the use of the charcoal. According to anembodiment of the present invention, porous materials such as silica andzeolite other than charcoal may be used in the conversion into FAME.

The foregoing method for producing biodiesel according to an embodimentof the present invention overcame disadvantages of thetransesterification process for producing biodiesel of the related art,and seems to overcome drawbacks of a transesterification reaction underactive development in the current R&D stage.

According to an embodiment of the present invention, biodiesel may beobtained through a continuous process.

According to an embodiment of the present invention, a biodieselconversion process may be effectively performed regardless of the amountof free fatty acids, unlike the process of the related art in which theprocess and the process operation are changed depending on the amount offree fatty acids (FFAs) present in oils.

In addition, according to an embodiment of the present invention, sincethe catalyst used in the transesterification reaction process is notused, the biodiesel conversion process may be constructed in a manner inwhich pretreatment and main treatment are integrated. Further, accordingto an embodiment of the present invention, the integration type ofpretreatment/main treatment process may fundamentally prevent thegeneration of waste water and the loss of biodiesel (FAMEs).

Further, an embodiment of the present invention is characterized in thatthe reaction is performed at normal pressure, unlike atransesterification process through a high-temperature/high-pressuresupercritical reaction which is currently under R & D.

According to an embodiment of the present invention, carbon dioxide isused in the process, which shows a definite contrast to thecommercialized transesterification process of the related art and thetransesterification process under R & D. This is an environmentallyfriendly process, which corresponds to the effect according to anembodiment of the present invention.

Further, according to an embodiment of the present invention, a definiteenergy saving effect may be exhibited since the biodiesel may be morequickly produced as compared with the commercial process of the relatedart. Particularly, since biodiesel (FAMEs) is produced from onlymethanol and oils as reactants, the costs for distilling purificationmay be expected to be remarkably saved.

The conversion of fatty acid alkyl esters which are generated from thetransesterification reaction performed in the presence of a refractoryporous material according to an embodiment of the present invention maybe 90% or higher, preferably 95% or higher, and more preferably 98% orhigher.

Contents other than the above descriptions may be added or deleted asnecessary, and thus are not particularly limited herein.

Hereinafter, although preferable examples are provided to helpunderstandings of the present invention, the following examples areprovided merely to illustrate the present invention, but the scope ofthe present invention is not limited to the following examples.

Examples 1-16

At conditions as shown in Table 1 below, oils and C₁-C₁₂ aliphaticalcohols were subjected to a transesterification reaction in acontinuous type in the presence of a refractory porous material, and thethus generated fatty acid alkyl esters and glycerol were collected toproduce biodiesel. Particularly, soybean oil for Examples 1 to 14,jatropha oil for Example 15, and extracted lipid from beef tallow andlard for Example 16 were used as the oils.

Here, the conversion of the generated fatty acid methyl ester (FAME) wasmeasured as follows.

<FAME Conversion>

The FAME conversion was obtained by using an analysis value throughGC/MS. The ASTM D6751 or EN14214 standard is acceptable for analysis ofbiodiesel. Particularly, the FAME yield was obtained by using EN14103(determining the ester and linoleic acid methyl ester content). Besides,EN14106/ASTM D6584 was used to determine glycerin and mono-, di-, andtriglyceride contents.

TABLE 1 Weight ratio of Reaction Reaction FAME oil to Charingtemperature pressure Retention conversion Classification Oils AlcoholsPorous material alcohol gas (° C.) (mmHg) time (min) (%) Example 1Soybean MeOH Al₂O₃ 1:0.2 CO₂ 400 760 1 98 oil Example 2 Soybean MeOHAl₂O₃ 1:0.2 CO₂ 350 760 1 99 oil Example 3 Soybean MeOH Al₂O₃ 1:0.2 CO₂450 760 1 99 oil Example 4 Soybean MeOH Al₂O₃ 1:0.1 CO₂ 400 760 1 95 oilExample 5 Soybean MeOH Al₂O₃ 1:0.4 CO₂ 400 760 1 99 oil Example 6Soybean MeOH Al₂O₃ 1:0.6 CO₂ 400 760 1 99 oil Example 7 Soybean MeOHAl₂O₃ 1:0.2 CO₂ 400 1,520 1 99 oil Example 8 Soybean MeOH Al₂O₃ 1:0.2CO₂ 400 10 1 99 oil Example 9 Soybean MeOH Al₂O₃ 1:0.2 CO₂ 400 760 0.199 oil Example 10 Soybean MeOH Al₂O₃ 1:0.2 CO₂ 400 760 2 99 oil Example11 Soybean MeOH Al₂O₃ 1:0.2 N₂ 400 760 1 95 oil Example 12 Soybean MeOHCharcoal 1:0.2 CO₂ 400 760 1 99 oil Example 13 Soybean MeOH MgO—CaO/1:0.2 CO₂ 400 760 1 98 oil Al₂O₃ Example 14 Soybean EtOH Al₂O₃ 1:0.2 CO₂400 760 1 99 oil Example 15 Jtropha oil MeOH Al₂O₃ 1:0.2 CO₂ 400 760 198 Example 16 beef MeOH Charcoal 1:0.2 CO₂ 400 760 1 99 tallow/lard

Comparative Example 1

Following the related art, biodiesel was produced by performing atransesterification reaction at a reaction temperature of 65° C. for 30hours while H₂SO₄ was used as an acidic catalyst. Here, the conversionof the generated fatty acid methyl esters (FAMEs) was 94%.

Comparative Example 2

Following the related art, biodiesel was produced by performing atransesterification reaction at a reaction temperature of 65° C. for 2hours while NaOH was used as a basic catalyst. Here, the conversion ofthe generated fatty acid methyl esters (FAMEs) was 94%.

Comparative Example 3

Biodiesel was produced by performing a transesterification reactionthrough the same method as in Example 1 except that a catalyst-freethermodynamic conversion method was applied for a reaction time of 300minutes or more by using bubbling instead of a porous filler while notusing the acidic or basic catalyst of the related art. Here, theconversion of the generated fatty acid methyl esters (FAMEs) was 91%. Inthis regard, an example of the results is shown in FIG. 15. In FIG. 15,ME represents methanol, TG represents triglyceride, DG representsdiglyceride, and MG represents monoglyceride.

As shown in Table 1, in Examples 1 to 16 in which, following the presentinvention, a transesterification reaction was performed in the presenceof a refractory porous material while acidic and basic catalysts werenot used, the reaction time was about 1 minute and the conversion was95% or more and more favorably 99% or more, resulting in a highconversion in a short time for each of the examples. While, in Examples1 and 2 in which, following the related art, acidic and basic catalystswere used, the conversion was merely about 94% for each of the examples.In the case of Example 3 in which a thermo-chemical conversion reactionwas performed without charging with a porous material, the conversionwas merely 91% even for a long reaction time of 300 minutes or more.

Meanwhile, FIG. 16 shows a mass chromatogram obtained by performing gaschromatography-mass spectroscopy (GC-MS) on products, which wereprepared from a transesterification reaction using beef oil and pork oilin Example 16. As confirmed in FIG. 16, in Example 16 in which,following the present invention, the transesterification reaction wasperformed by using beef tallow and lard while not using separate acidicand basic catalysts, the conversion into biodiesel (fatty acid methylesters, FAMEs) was effectively achieved without the detection of fattyacids corresponding to initial components.

While this invention has been described in connection with what ispresently considered to be practical embodiments, it is to be understoodthat the invention is not limited to the disclosed embodiments, but, onthe contrary, is intended to cover various modifications and equivalentarrangements included within the spirit and scope of the appendedclaims.

1. A method for producing biodiesel, the method comprising generatingfatty acid alkyl esters and glycerol by a transesterification reactionof oil and an aliphatic alcohol in a presence of a refractory porousmaterial.
 2. The method of claim 1, wherein a temperature of thetransesterification reaction is controlled such that thetransesterification reaction proceeds in a presence of the porousmaterial, by raising energy levels of the oil and the aliphatic alcoholthrough a supply of heat energy; and wherein the temperature of thetransesterification reaction is controlled such that the fatty acidalkyl esters are generated in a gas phase and thermal cracking of theoil is not generated.
 3. The method of claim 2, wherein the temperatureof the transesterification reaction is 350 to 500° C.
 4. The method ofclaim 3, wherein the weight ratio of the oil to the alcohol is 1:0.05 to1:1.
 5. The method of claim 4, wherein a retention time of thetransesterification reaction is 0.1 to 5 minutes.
 6. The method of claim1, wherein the transesterification reaction is performed in a gasatmosphere of at least one of nitrogen, argon, or carbon dioxide.
 7. Themethod of claim 1, wherein a pressure of the transesterificationreaction is 10 mmHg to 10 atm.
 8. The method of claim 1, wherein thetransesterification reaction is performed in a heterogeneous phasereaction.
 9. The method of claim 1, wherein the transesterificationreaction is performed in a continuous process.
 10. The method of claim1, wherein the refractory porous material is at least one of alumina(Al₂O₃), zeolite, activated carbon, charcoal, or silica.
 11. The methodof claim 1, wherein the refractory porous material includes a mesoporousmaterial, a macroporous material, or both thereof.
 12. A method forproducing biodiesel, the method comprising: inducing atransesterification reaction between oil and an aliphatic alcohol bycontinuously supplying the oil and the aliphatic alcohol into a reactorcharged with a refractory porous material; and collecting gas-phasefatty acid alkyl esters and glycerol, which are generated by thetransesterification reaction.
 13. The method of claim 12, wherein in theinducing of the transesterification reaction, a purge gas iscontinuously supplied together with the oil and the aliphatic alcohol,the purge gas being at least one of nitrogen, argon, or carbon dioxide.14. The method of claim 12, wherein a temperature of the reactor iscontrolled such that the transesterification reaction proceeds in apresence of a porous material, by raising energy levels of the oil andthe aliphatic alcohol through a supply of heat energy; and wherein thetemperature of the transesterification reaction is controlled such thatthe fatty acid alkyl esters are generated in a gas phase and thermalcracking of the oil is not generated.